The increase in oil prices, the demand for urban vehicles, the mega cities and the new approach to sustainable transport has led to a trend towards the use of alternative energy sources for cars, which resulted in hybrid vehicles (EVs). Estimates suggest that by 2020, EVs will account for 7% of the global transport market. However, there are concerns about the supply of critical elements needed for these vehicles batteries, as there is a threat to the availability of lithium needed for production of such batteries. This situation has changed the focus on the sources from which this metal is obtained, in order to ensure its continuous supply, arising thus the possibility to reuse and recycle these batteries. With over 70% of EVs probably introduced in 2015 based on the chemistry of lithium-ion (Li-ion) batteries, lithium recycling has become a crucial topic in the automotive industry.
In the future, many challenges are likely to have an impact on lithium supply. Although there are enough lithium resources available in the World to meet the demand, nearly 70% of global lithium deposits are located in Argentina, Bolivia and Chile. This causes an inherent risk due to the accessibility of raw materials that are only available in a specific region, which can greatly affect supply and have an impact on battery prices.
Lithium is also consumed in numerous applications or sectors, such as construction, pharmaceuticals, ceramics and glass, so that consumption in the automotive industry is only a small fraction. Heretofore, batteries account only for a quarter of the current lithium consumption, although it is expected to reach 40% by 2020. Lithium represents only a small fraction of the cost of the raw materials needed for batteries manufacture.
Intergovernmental initiatives are being carried out in order to ensure lithium resources. Vehicle manufacturers and national governments are treating lithium as a source of future energy and have begun strengthening alliances to safeguard their needs. Toyota and Magna International-Mitsubishi have strengthened links with lithium exploration companies and have heavily invested to develop lithium deposits in Argentina and secure resources to strengthen their needs. Japan has signed agreements with the Bolivian government to provide economic aid in exchange for lithium and other rare metals supplies. Original equipment manufacturers are seeking to overcome lithium dependence by reusing lithium batteries for other applications and by recycling batteries after their life cycle have been completed. However, recycling batteries makes no economic sense. Batteries contain only a small fraction of lithium carbonate in weight percentage and are inexpensive compared to cobalt or nickel. The average cost associated to lithium production in lithium ion batteries is less than 3% of the production cost. The intrinsic value in the recycling business comes from more valuable metals, such as cobalt and nickel, which are more expensive than lithium. Due to a lower lithium demand and lower prices, lithium used in consumer batteries is not completely recycled.
Recycled lithium is five times more expensive than lithium produced from mineral sources, so recycling is not competitive for companies in the sector. However, with an increasing number of EVs entering the market, future shortages are foreseeable, which can lead to recycling being a necessity for the supply of batteries materials.
The battery recycling market is conditioned mainly by price, because technology is not a critical differentiator. All key participants use the same technology level in their offered products. Therefore, price is the key differentiating factor, which reduces the benefit for battery recycling companies in a competitive environment.
Specialized processes and small-scale recycling plants nearby vehicle manufacturers are likely to be the trend in the future. The main obstacle hindering such projects is the nature of the financial investments required by participants to develop specialized waste collection. Given that the market is still unexplored, the specific impacts and the total benefit of these investments are unknown and, therefore, would create ambiguity and uncertainty when making such commitments.
With lithium recycling just in its beginning, there is no infrastructure in the world, except for some pilot plants currently in development stage.
The lack of standards in the batteries chemistry and a changing environment with respect to different elements under investigation for the production of batteries other than lithium, make recycling of components uncertain for recyclers.
The use of lithium ion batteries in electronic devices and electric vehicles is continuously increasing. This type of battery is one of the most commonly used because of its high energy density, high voltage, long of charge and discharge cycles, wide temperature range, decreased risk of explosion and absence of memory effect [1].
Lithium ion batteries are composed of a cathode, an anode, organic electrolytes and a separator film. The cathode generally contains an Al foil covered by a thin layer of LiCoO2 powder and the anode is formed by a Cu foil covered by a layer of graphite. Both electrodes are separated by a film and are coated with a compound electrolyte with a Li salt, soluble in organic solvents [1]. The increase in lithium ion battery production has made recycling of its components increasingly important, since its unsafe disposal can cause serious environmental problems [2]. Hydrometallurgical processes are among the processes used for recycling batteries, which have as main advantages the full, high-purity recovery of metals, low energy requirement, and minimum generation of aqueous and gaseous waste [2]. The reductive dissolution of LiCoO2 has been studied using inorganic acids, such as H2SO4 [3], HNO3 [4] and HCl [5]; alkalis, wherein the most used compound has been NaOH [6], and organic acids, such as citric, malic and aspartic acids. Li et al. (2013) conducted a comparative study of the operating variables of the reductive dissolution of LiCoO2 process using citric, aspartic and malic acids. They reported near 100% recoveries for Li and above 90% for Co using citric acid and malic acid. In the case of aspartic acid, lower dissolutions were obtained due to the weak character of the acid and its low solubility in water [1].
Acetic acid is an organic acid produced by synthesis and by bacterial fermentation, which has high solubility in water and is biodegradable. In the present invention, as detailed below, a study of the effect of operating variables on the acid dissolution of lithium and cobalt mixed oxide from lithium ion batteries is described. Several documents on the dissolution of LiCo2 are known. The following are among them, and their problems compared with the development of the present invention are presented below:
1) Novel Approach to Recover Cobalt and Lithium from Spent Lithium-Ion Battery Using Oxalic Acid
Authors: Xianlai Zeng, Jinhui Li, Bingyu Shen
In this work, the authors dissolve LiCoO2 with oxalic acid.
The inventors have carried out experimental tests in the conditions of this work and in other conditions and confirmed that during the leaching process with oxalic acid and oxalic acid-hydrogen peroxide as leaching agents, at concentrations lower or greater than stoichiometric, oxalate cobalt precipitates; noting that, for concentration values closer to stoichiometric, LiCoO2 solutions of very low concentration are achieved. Moreover, cobalt oxalate precipitation is greater with increasing concentration of oxalic acid and temperature. Moreover, it is not easy to separate the unreacted oxide and the cobalt oxalate co-precipitate. This requires multistage separation and purification. The inventors have carried out several tests attempting to separate those using various chemical agents, for example inorganic acids and bases, organic solvents, etc. and, in no case was it possible to completely dissolve the CoC2O4 or the LiCoO2; From these results, it can be concluded that its industrial feasibility is very low.
Moreover, and very importantly, the authors of this work (Xianlai et al.) reflect the cobalt oxalate precipitation, under “3.2. Optimizing the process for leaching cobalt and lithium”.
Another aspect to be noted is that, in this work, the authors carried out a complete grinding of the cathode, i.e. the sample contains: LiCoO2 and Al, therefore, during the dissolution stage with oxalic acid and hydrogen peroxide, Al is also leached (reaction 5) and will interfere with and/or contaminate the obtained products, as these authors did not perform a separation stage prior to dissolution or during precipitation or retrosynthesis. Therefore, the obtained products contain aluminum or a compound thereof. Aluminum is part of the cathode as a support, and LiCoO2 is adhered thereto, which is clearly seen in the sample as “bright spots” (in the graphic summary “Highlights”) and whose contents are also reported by the authors in Table 1 and FIG. 1. Cobalt oxalate contaminated with coal also appears in the products.
2) Recovery of Cobalt and Lithium from Spent Lithium Ion Batteries Using Organic Citric Acid as Leachant
Authors: Li Li, Jing Ge, Feng Wu, Renjie Chen, Shi Chen, Borong Wu
In this work the authors carry out pretreatments of the sample, which involve freezing the battery to −197° C. using liquid nitrogen, manually opening the battery (at low temperature), treatment with solvent and calcination at 700° C. for 5 h. After this pretreatment of the sample, the authors carry out the dissolution with citric acid and hydrogen peroxide.
Finally, Li et al. do not attempt any experiment to study the separation of Li and Co dissolved with citric acid. It should be noted that that the citric acid is a strong ligand which produces highly stable complexes with Co, therefore, this ligand is difficult to displace and its compounds are highly soluble and stable; the authors do not report results on this separation.
Differences between this process and the one disclosed herein are: the dismantling of the sample and the separation of its components do not require steps of freezing, no solvents are used and the sample is not calcined. The dissolution carried out in the process disclosed herein is of the mixed oxide only, yielding, in some cases, leaching greater than 95%, followed by a separation process with pure filtrates. Given that the authors of this work (Li et al.) do not carry out the separation of Li and Co, this process cannot be evaluated. That is, Li et al. only reach the solution containing lithium and cobalt by leaching with citric acid, not with acetic or tartaric acid, as is done herein. In addition, as mentioned above, they do not recover both metals; although the abstract mentions that said citrates of Li and Co are obtained, the complete flow chart of the process they propose (FIG. 2) ends with a solution containing Li and Co previously dissolved with citric acid; they do not propose any process for the separation of the obtained products in solution.
Therefore, even combining the process in Li et al. with the one in Xianlai, the results obtained with the method of the present invention would not be achieved, since in the second stage of the present method, almost complete dissolutions of LiCoO2 are obtained, without the presence of other interfering elements.
3) The Re-Synthesis of LiCoO2 from Spent Lithium Ion Batteries Separated by Vacuum-Assisted Heat-Treating Method
Authors: Mi Lu, Houan Zhang, Bingchen Wang, Xiaodong Zheng, Changsong Dai
The work of Lu et al. aims at re-synthesizing LiCoO2, but the previous process to obtain the powder which is then dissolved, it is not industrially feasible as it passes through several previous steps, such as heating the sample to 600° C. in vacuum, followed by further heating to 800° C. to remove anode coal and/or the adhesive used to adhere the LiCoO2 to the aluminum foil. The process then proceeds to another quite costly step of grinding for 2 h in a mill, then ending with a final calcination step at 750° C. for 15 hours, whereby re-synthesis of the oxide is achieved.
4) Battery Recycling Technologies: Recycling Waste Lithium Ion Batteries with the Impact on the Environment in-View.
Authors: Chunxia Gong and Lixu Lei
This work is a review where a description of all treatment processes on lithium ion recycling of batteries is made. In this work, it is recommended that the dissolution with solvent prior to the dissolution is the most recommended technique. This is an advantage of our process.
The authors of this review describe various hydrometallurgical processes that combine the dissolution of the mixed oxide with various inorganic acids and the compounds of Li and Co are separated and/or precipitated using NaOH or organic solvents. Finally, they propose as more viable a hydrometallurgical process (FIG. 4, from Chunxia Gong and Lixu Lei) containing alkaline leaching, treatment with solvent to dissolve the powder with sulfuric acid, then recovering the Co with oxalic acid and Li with Na2CO3. However, the leaching of the powder with H2SO4 is low unless high concentrations of this acid are used or unless the acid is mixed with hydrogen peroxide; if so, the high concentration of sulfuric acid would decompose the oxalic acid and sodium carbonate, which are the used precipitating agents. With the method of the present invention, as detailed below, only Li2CO3 precipitates with sodium carbonate after precipitation of Co with NaOH, whereby the excess acid is neutralized beforehand.
5) Patent “Method for Preparing LiCoO2-Coated NiO Cathodes for Molten Carbon Fuel Cell”. U.S. Pat. No. 6,296,972 B1
Authors: Hong et al.
In this patent, the authors apply a known method for synthesis of materials as is the “sol gel” method to a novel type of NiO (Ni oxide) cathode coated with a mixed oxide of lithium and Co. This LiCoO2 synthesis process was developed for other cathodes, whereby its teachings cannot be applied to the cathodes of the present invention.
Another aspect of the method of the present invention, as detailed below, is re-synthesizing again the mixed oxide of lithium and Co by the sol-gel method from solutions obtained from acetic or citric acid leaching of this spent oxide, since high dissolutions of the mixed oxide of lithium and cobalt are achieved and said oxide is composed of a solution of Co and Li (as oxide precursors) with minimal impurities, as the method of the present invention makes a prior separation of the components of lithium ion battery; there are no other components that can be dissolved. Afterwards, the sol-gel method is carried out as indicated in the art, without the need of adding a binder.
It should be noted that the process of the present invention, as will be detailed later, has a dissolution stage in which only carboxylic acids are used, the decomposition of which in the final calcination step to generate the oxide produces CO2, which can be captured and properly treated or reprocessed. That is, the complete process has a low environmental impact and is economically viable.